They come with a little pad that stops the hose rattling when you're riding, it tends to fall off when you undo the fitting,
A wrap of insulting tape sorts it out, or make a little pad out of some rubber to sit behind the hose in the guide

What khani said. But any small square of rubber will do. If you look carefully you'll see the indentation in the lowers where the rubber block is meant to fit. It's about 8x5x3mm if you're going to cut a replacement.